The term “electrode contact” will be used herein to describe a conductive element in the lead. The term “lead” will be used herein to describe the device that may be connected to an implantable stimulator for carrying stimulation current from the stimulator to the electrode contact on the lead. The term “electrode” will be used to describe that portion (usually the distal end) of the lead that includes the electrode contact(s). The term “electrode array” will refer to that portion of the lead having a multiplicity of electrode contacts.
Spinal cord stimulation is a well accepted clinical method for reducing pain in certain populations of patients. An SCS system typically includes an Implantable Pulse Generator (IPG), an electrode, electrode lead, and an electrode lead extension. The electrode is implanted along the dura of the spinal cord, and the IPG generates electrical pulses that are delivered, through the electrode contacts, to the dorsal column and dorsal root fibers within the spinal cord. Individual electrode contacts are arranged in a desired pattern and spacing in order to create an electrode array. Individual wires within the electrode lead connect with each electrode contact in the array. The electrode lead exits the spinal column and generally attach to an electrode lead extension. The electrode lead extension, in turn, is typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG is implanted.
Spinal cord stimulators and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in U.S. Pat. No. 3,646,940 issued Mar. 7, 1972 for “Implantable Electronic Stimulator Electrode and Method” that provides timed sequenced electrical impulses to a plurality of electrodes. As another example, U.S. Pat. No. 3,724,467 issued Apr. 3, 1973 for “Electrode Implant For The Neuro-Stimulation of the Spinal Cord,” teaches an electrode implant for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided on which a plurality of electrode contacts are formed. The electrode contacts are connected electrically to an RF receiver, which is also implanted.
Most of the electrode arrays used with known SCS systems employ between 4 and 16 electrodes. Electrodes are selectively programmed to act as anodes, cathodes, or left off, creating a stimulating group. The number of stimulation groups available, combined with the ability of integrated circuits to generate a variety of complex stimulation pulses, presents a huge selection of stimulation parameter sets to the clinician. When an SCS system is implanted, a “fitting” procedure is performed to select an effective stimulation parameter set for a particular patient.
In order to achieve an effective result from spinal cord stimulation, the lead or leads should be placed in a location such that the electrical stimulation will affect the targeted nerves and cause paresthesia. The paresthesia perceived by the patient and induced by the stimulation masks the pain that is the target of treatment. If a lead is not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy. During surgery, the physician places the leads in a very careful manner in order to locate the electrode contacts proximal to neural elements that are the target of the stimulation. During and after placement, stimulation energy is delivered to verify that the leads are indeed stimulating the appropriate neural elements.
If the lead(s) happen to shift position after implant, the targeted neural fibers may no longer be appropriately stimulated. At best, this can require electrical reprogramming to restore therapy or, at worst, surgical revision, where a second surgery is required and the leads must be manually readjusted. In the first case, the physician may have only a suspicion that a lead has shifted position, based on patient reporting of paresthesia, which is not foolproof. Also, attempting to reprogram the leads based on paresthesia locations can be challenging.
There are two major types of electrodes used for spinal cord stimulation: (1) percutaneously implanted in-line electrodes, requiring local anesthesia for implant, and (2) paddle-shaped electrodes, requiring major surgery for implantation.
The first type of electrode, i.e., the in-line electrode, comprises thin, cylindrical-style electrodes. Such in-line or cylindrical-style electrodes are easier and less invasive to implant, typically requiring only local anesthesia and the use of a large gauge needle, for example a 15 gauge Touhy needle. Disadvantageously, such in-line electrodes are not as stable as a paddle-shaped electrodes, as they may be more easily pulled out or pushed into the tissue and are therefore prone to migration.
The second type of electrode, i.e., the paddle-shaped electrode, provides a large-area electrode surface to contact the body tissue. Advantageously, such paddle-style electrodes are more stable than in-line electrodes, after implant. Moreover, such paddle-style electrodes provide a platform for multiple sets of electrodes in many possible configurations to thereby optimize electrode programming and clinical results. In contrast, the percutaneous in-line electrodes can only combine electrodes in a vertical or linear row. Disadvantageously, however, the paddle style electrodes require complex major surgery and must be precisely maneuvered into place during implantation.
An insertion needle for introduction of a paddle-style electrode near the spinal column or other nervous system is described in U.S. Pat. Nos. 6,309,401, 6,553,264, and 6,249,707, all having the same assignee and all incorporated herein by reference.
U.S. Pat. No. 6,319,241, incorporated herein by reference, discloses techniques for implanting a lead having therapy delivery elements, such as electrodes or drug delivery ports, within a vertebral or cranial bone so as to maintain these elements in a fixed position relative to a desired treatment site. The described techniques in the '241 patent focus on the fixation method for the electrodes or drug delivery ports.
U.S. Pat. No. 6,027,456, incorporated herein by reference, describes an apparatus for assisting in the placement of the spinal cord stimulation lead with respect to the dorsal column of a patient. The invention described in the '456 patent focuses on detecting evoked potentials which result from the controlled stimulation of spinal nerves. An insertion tool used to assist in steering the lead in place is not described.
A need exists for an improved simple-to-use implant tool that affords steerability of a paddle-style electrode during insertion and implantation without the risk of damaging the insulation and/or conductors of the paddle-style electrode.